The present invention relates generally to internal combustion engines. More specifically, the present invention relates to a process for operating an internal-combustion engine with a supercharger or compressor which can be cut out, and to a device for carrying out the process.
Increasingly stringent requirements for reducing harmful materials in exhaust gases are imposed on internal-combustion engines, especially those in vehicles. Diesel-type internal combustion engines used as vehicle drives have, in comparison with gasoline engines, lower concentration values of carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas. However, in diesel engines with optimum consumption, the emissions of nitrogen oxides (NO.sub.x) are too high.
These emissions of nitrogen oxides can be reduced by the use of various measures, for example by catalytic oxidation and washing-out, or by the injection of water into the combustion chamber to lower the combustion temperatures, or by returning exhaust gases into the combustion chamber. The combustion temperatures can also be lowered by this last-mentioned measure. Such a returning of exhaust gas can be used both in diesel and in gasoline engines.
Compressors which can be cut in and out of an engine system are known from a publication in "Schnelle Motoren" ["High-speed engines"] by Helmut Hutten (6th revised edition, page 264). These compressors can be cut in and out via a coupling, that is to say, when they are cut out in the case of a low power requirement, the engine already runs in suction operation and, because of its design, has a lower ejection of harmful materials than a non-supercharged engine of the same maximum power.
A primary object of the present invention is to use, on an engine with a compressor which can be cut in, the advantages, known per se, of exhaust-gas return.
The above-mentioned object and other objects of the present invention are achieved, first, by a series of process steps according to the present invention. During idling and under partial load the compressor is cut out and combustion air is sucked in from the atmosphere and part of the exhaust gases is mixed with the stream of intake air via an exhaust-gas return line, a supercharger delivery line of the compressor being closed by a shut-off member. Under higher partial load, and full load, the compressor compresses combustion air from the atmosphere and supplies it to the internal-combustion engine through an intake pipe, while the exhaust-gas return and the intake of air from the atmosphere are interrupted by the shut-off member.
Secondly, the objects of the present invention are achieved by a device according to the present invention, in which an exhaust-gas return line opens, opposite the supercharger delivery line, into the intake line. A shut-off member is arranged so that during suction operation the supercharger delivery line is closed, and during supercharging operation the intake line and the exhaust-gas return line are closed.
Such an arrangment ensures that during idling and under lower partial load and with the compressor cut out, that is to say in a state in which an exhaust-gas return is desired during the intake of air from the atmosphere, this return can take place. On the other hand, by actuating the shut-off member, with the compressor cut in, under a higher partial load and full load, when an exhaust-gas return is not required, this return can be prevented in a simple way. The shut-off member is actuated automatically when the compressor is either cut in or cut out. With the compressor cut out, the shut-off member will close the supercharger delivery line and open the intake line and the exhaust-gas return line. When compressed air is supplied to the engine, that is to say when the compressor is cut in, the shut-off member automatically opens the supercharger delivery line and closes the intake-air line and the exhaust-gas return line.